One year ago, a massive earthquake spawned a tsunami that nearly destroyed Japan’s Fukushima Daiichi nuclear plant, further frightening people who had been wary of nuclear power since accidents at Three Mile Island in 1979 and Chernobyl in 1986.

But a small group of scientists, entrepreneurs and advocates see the post-Fukushima era as the perfect opportunity to get the United States to consider a proposal they have made with no success for years. What about trying a new fuel, they say, and maybe a new kind of reactor?

The proposed fuel is thorium, an abundant silver-gray element named for the Norse god of thunder. It is less radioactive than the uranium that has always powered U.S. plants, and advocates say that not only does it produce less waste, it also is more difficult to turn into nuclear weapons.

They’re pushing the idea of adapting plants to use thorium as a fuel or replacing them with a completely new kind of reactor called a liquid-fluoride thorium reactor, or LFTR (pronounced “lifter”). The LFTR would use a mixture of molten chemical salts to cool the reactor and to transfer energy from the fission reaction to a turbine.

Proponents say such a system would be more efficient and safer than existing plants, which use pressurized water to cool uranium fuel rods and boiling water or steam to transfer the energy they create.

“A molten-salt reactor is not a pressurized reactor,” said John Kutsch, director of the Thorium Energy Alliance, a trade group based in Harvard, Ill. “It doesn’t use water for cooling, so you don’t have the possibility of a hydrogen explosion, as you did in Fukushima.”

Kutsch and others say that a thorium-fueled reactor burns hotter than uranium reactors, consuming more of the fuel. “Ninety-nine percent of the thorium is burned up,” he said. “Instead of 10,000 pounds of waste, you would have 300 pounds of waste.”

‘Small boatloads of fanatics’

Although the idea of thorium power has been around for decades — and some countries are planning to build thorium-powered plants — it has not caught on with the companies that design and build nuclear plants in the United States or with the national research labs charged with investigating future energy sources.

“There are small boatloads of fanatics on thorium that don’t see the downsides,” said Dan Ingersoll, senior project manager for nuclear technology at the Oak Ridge National Laboratory in Tennessee. For one thing, he said, it would be too expensive to replace or convert the nuclear power plants already running in this country: “A thorium-based fuel cycle has some advantages, but it’s not compelling for infrastructure and investments.”

He also pointed out that thorium would still have some radioactive byproducts — just not as much as uranium and not as long-lived — and that there is no ready stockpile of thorium in the United States. It would have to be mined.

Overall, he says the benefits don’t outweigh the huge costs of switching technologies. “I’m looking for something compelling enough to trash billions of dollars of infrastructure that we have already and I don’t see that.”

Thorium advocates such as Kirk Sorensen, a former NASA engineer who is now chief executive of Huntsville, Ala.-based Flibe Energy, are not deterred.

“We recognize this is a new and different technology, and developing it is significantly different from the existing nuclear industry,” Sorensen said. “Part of the problem is that nuclear only means one thing in the public and [U.S.] government’s mind.”

Thorium exists in the ground as thorium oxide and is three to four times as abundant worldwide as uranium, according to a 2005 report from the International Atomic Energy Agency. Thorium is less radioactive than uranium, and it emits alpha particles, which are less biologically harmful than uranium’s gamma particles. That makes thorium easier to store safely.

With an extremely high melting point (over 6,000 degrees), thorium has been used in portable gas lanterns, high-temperature ceramic products and aerospace applications. But because of its radioactivity and the development of alternative materials, most uses of the element were phased out.

Once a working experiment

Half a century ago, however, the United States was taking a serious look at thorium as a nuclear fuel. It was used at a molten-salt reactor that government scientists built and ran from 1965 to 1969 at Oak Ridge.

But after India detonated a nuclear bomb in 1974 with plutonium extracted from a reactor designed for non-weapons use, fears of proliferation convinced successive U.S. administrations to cut back on experimental nuclear programs. The thorium-fuel project was mostly forgotten. Instead, all subsequent nuclear plants were designed to use uranium, the fuel that powers all 104 reactors operating in the United States today.

Almost all the U.S. plants are at least 25 years old; some are approaching 50. With the federal government unable to come up with a permanent waste disposal site, spent fuel rods — which remain radioactive for thousands of years — are piling up at each reactor site.

Nevertheless, utilities have been preparing to build 20 to 30 similar reactors to replace the older ones. (Earlier this month, the Nuclear Regulatory Commission approved Atlanta-based Southern Co.’s proposal to build two such reactors in Georgia. )

For the past few years, Sorensen has been trying to convince them to build LFTRs instead. He posts technical documents from the Oak Ridge thorium reactor on his blog, Energy from Thorium. Last year, he left his day job at Teledyne Brown Engineering to start Flibe, the name of which is derived from the mixture of fluoride, lithium and beryllium salts used in a LFTR.

“We can look back to Oak Ridge,” he says, to “rebuild the capability that existed in 1974.”

Sorensen says a LFTR using a mixture of thorium as a fuel plus either uranium or plutonium to kick-start the reaction could produce higher core temperatures at lower pressures than steam reactors, meaning it would not need as many safety and cooling systems.

Even better, he says, LFTRs could be configured to consume the spent fuel that is sitting around the country at nuclear sites.

Other entrepreneurs are taking a different tack. McLean-based Lightbridge wants to mix thorium and uranium to slightly boost the output of existing nuclear plants. Lightbridge is helping the Russian government build such a program, said Seth Grae, the company’s president and chief executive.

But most U.S. nuclear energy industry executives are wary of both approaches to thorium, saying that neither utilities nor investors are eager to gamble on an unfamiliar technology.

“Customers are telling us, ‘Let’s focus on taking [financial] risk off the table, not putting it back on,’ ” said Chris Mowry, president and chief executive of Babcock & Wilcox, a Lynchburg-based firm that is building smaller reactors fueled by uranium. “We view [thorium] as something that’s down the road. It’s more of the science-project phase.”

Military applications

Seeking energy sources not tied to petroleum, the Pentagon’s Defense Advanced Research Projects Agency (DARPA) announced in 2010 that it was proposing a plan to make both jet fuel and electricity from small mobile nuclear plants. Sorensen says he has talked with Pentagon officials about using thorium for such reactors in hostile areas. Since thorium is less adaptable for weapons purposes, the reactor would be safe enough to leave behind for civilian use when U.S. troops pull out.

“Thorium potentially would offer some way to mitigate that challenge of security and safety if we do convince ourselves to put nuclear plants in these locations,” said Col. Paul E. Roege, chief of the Army’s operational energy cell at the Pentagon.

Roege said the Pentagon is considering the pros and cons of thorium. One drawback, he said, is that engineers aren’t familiar with it. “We have lots of uranium reactors, people are comfortable with them, and we have a mature technology,” Roege said. “That’s not the case with thorium reactors.”

Ingersoll, the Oak Ridge scientist who is skeptical of thorium as a new fuel, agreed that it cannot practically be used to make a nuclear weapon. He cautioned, however, that it is still a radioactive material: “It doesn’t eliminate the [nuclear waste] product. It’s just not as bad.”

Ingersoll said that thorium-powered reactors make more sense for countries that don’t have access to the plentiful reserves of uranium that exist in the United States.

Chinese government officials announced in February 2011 that they are developing a thorium-based reactor and will have it operating within the next 15 or 20 years. India has plans to use thorium in some of its existing reactors.

Kutsch argues that the United States could be losing out on developing an important technology. He has been lobbying members of Congress to introduce legislation that would reclassify thorium as a special industrial material, rather than a nuclear material. “Our legislation would say thorium is not like uranium and plutonium,” he said. “It can be safely and handled and stored, like ammonia or fertilizer.”

Kutsch is also pushing for another bill that would direct the Nuclear Regulatory Commission to develop rules for the use of thorium. That would give U.S. companies an opening to start using thorium in existing reactors.

Rep. John Shimkus, the Illinois Republican who chairs a subcommittee that oversees nuclear waste disposal, says he will be introducing thorium legislation this year.

“For those who hate the [problem of] high-level nuclear waste,” Shimkus said in a phone interview, “thorium is a great response.”

Niiler is a freelance writer based in Chevy Chase.